1. Field of the Invention
The present invention relates to a sheet-feed perfecting press for printing both sides of a sheet.
2. Description of Related Art
FIG. 6 is a schematic view of a conventional printing press of this type. This printing press has a sheet feed unit 1, a printing unit 2, and a sheet discharge unit 3 (taking-off apparatus). In the printing unit 2, top surface printing devices (outer printing devices) 2a and 2c and back surface printing devices (inner printing devices) 2b and 2d, each having an ink arrangement K, a dampening arrangement D, a plate cylinder P, a rubber blanket cylinder B, and an impression cylinder I, are arranged alternately. A delivery cylinder T1 is disposed close to the top surface printing device 2a, and two intermediate cylinders T are disposed between the impression cylinder I for the back surface printing device 2b and the impression cylinder I for the top surface printing device 2c. Between the impression cylinder I for the back surface printing device 2d and the sheet discharge unit 3, three intermediate cylinders T are disposed. The impression cylinders I and the intermediate cylinders T have the same diameter, and are arranged on substantially the same horizontal plane.
In this printing press, a sheet 4 is supplied one after another by the sheet feed unit 1, and after an outer side 7 thereof being printed by the top surface printing devices 2a and 2c, and an inner side 8 thereof being printed by the back surface printing devices 2b and 2d, the printed sheet 4 is stacked by the sheet discharge unit 3. When the outer side 7 or the inner side 8 is printed by the printing unit 2, the outer side 7 is printed by the top surface printing device 2a, for example. Next, when the inner side 8 is printed by the back surface printing device 2b, the outer side 7, which has been printed by the top surface printing device 2a, is in contact with the impression cylinder I at a printing pressure point 5 where a pressure is applied to the sheet surface by the back surface printing device 2b. The length between the printing pressure point 5 for the top surface printing to the printing pressure point 5 for the back surface printing is shorter than or approximately equal to the length of the sheet 4.
FIG. 7 is a schematic view of another conventional printing press. In this figure, the same reference characters are applied to elements which are essentially the same as those shown in FIG. 6, and the duplicate explanation of these elements is omitted. For the printing press shown in FIG. 7, the impression cylinders I for the printing devices 2a, 2b, 2c and 2d each have a diameter larger than that of the plate cylinders P and the rubber blanket cylinders B, and are arranged somewhat in a zigzag form vertically. This printing press is different from the printing press shown in FIG. 6 in that only one intermediate cylinder T is disposed between the back surface printing device 2d and the sheet discharge unit 3. The distance between the printing pressure point 5 on the impression cylinder I for the top surface printing device 2a and the printing pressure point 5 for the back surface printing device 2b is approximately equal to or slightly longer than the length of the sheet 4.
In the above-described conventional printing presses, the outer side 7, which has been printed by the top surface printing device 2a, is in contact with the impression cylinder I at the printing pressure point 5 for the back surface printing device 2b. Therefore, the surface of the impression cylinder I is stained with ink, so that this stain stains the outer side 7 of the next sheet 4, resulting in a decrease in print quality. This poses a problem in that it is necessary to strictly take measures for preventing stains and to frequently perform work for removing stains. Also, the printing press shown in FIG. 6 requires a large size because the impression cylinders I and the intermediate cylinders T are arranged on the same plane.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide a sheet-feed perfecting press in which the above-described stains can be reduced, the degradation in print quality can be minimized, work for removing stains can reduced, and the machine size can be decreased.
To achieve the above object, the present invention provides a sheet-feed perfecting press which has a top surface printing device and a back surface printing device each having a plate cylinder and an impression cylinder and is provided with a plurality of printing pressure points at which a pressure is applied to the surface of a sheet at the time of printing, characterized in that an intermediate cylinder is provided between the adjacent printing pressure points of the plurality of printing pressure points.
Also, in the present invention, the diameter of the impression cylinder is preferably made larger than the diameter of the plate cylinder. The diameter of the intermediate cylinder is preferably made larger than the plate cylinder. Also, the diameter of a rubber blanket cylinder for applying a pressure to the surface of the sheet at the time of printing may be larger than the diameter of the plate cylinder.
Further, in the present invention, at least two intermediate cylinders are arranged between the plate cylinder and the impression cylinder, and the intermediate cylinders can be arranged in a zigzag form with respect to the horizontal line. Also, it is preferable that a grip change position where grip change of sheet to the intermediate cylinder is made be kept away from the printing pressure point.